how can i comment on jenkins scheduled build scripts?

Prefix the line with “#”.

As can be gleaned from the “Build periodically | Schedule” help (?) example:

Examples: 
# every fifteen minutes (perhaps at :07, :22, :37, :52)
H/15 * * * *
# every ten minutes in the first half of every hour (three times, perhaps at :04, :14, :24)
H(0-29)/10 * * * *

The scheduler inherits the same comment syntax as crontab